The field of the disclosure relates generally to composite materials and, more particularly, to bulk carbon nanotube and metallic composites.
At least some known carbon nanotubes (CNT) are formed from a one-atom thick sheet of graphite commonly referred to as “graphene”. The sheet is rolled into a cylinder that has a diameter of the order of a nanometer and a length on the order of a micrometer. Known CNTs exhibit extraordinary strength and electrical properties, and are efficient conductors of heat. The two most common types of CNTs are single-walled carbon nanotubes (SWCNTs) that are formed from a single layer of graphene, and multi-walled carbon nanotubes (MWCNTs) that are formed from multiple concentric cylinders or a graphene sheet that is rolled around itself.
CNTs are lightweight and have a very high elastic modulus. The conductive properties of CNTs depend upon the diameter and the chirality of the hexagonal carbon lattice extending along the tube. A slight change in the winding of the hexagonal lattice along the tube can result in the CNT functioning either as a metal or a semiconductor. For example, hexagonal rows that are parallel to the tube axis produce a metallic structure known as an “armchair” configuration. In contrast, alternating rows of carbon bonds around the tube circumference produce a semi-conducting structure known as a “zigzag” configuration. Although individual CNTs may be highly electrically conductive, high contact resistance between multiple CNTs results in low electrical conductivity of bulk CNT materials.